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Basic Facts About Colorado River Basin Fish

The Colorado River Basin is home to at least 14 native species of fish. Four of these fish are endangered—the Bonytail (Gila elegans), Razorback Sucker (Xyrauchen texanus), Colorado pikeminnow (Ptychocheilus lucius), and Humpback chub (Gila cypha). These fish evolved over millions of years in the Colorado River Basin, and are unique to the ecosystem.

Bonytails

Bonytails are dark gray, silver and white with small heads, large fins and streamlined bodies

Length: 16-18 inches, though some have been known to grow to 2 feet.

Diet: Insects and plant matter.

Lifespan: Bonytails can live as long as 50 years.

Reproduction: Bonytail spawn in spring and early summer at age of 5 to 7 years.

Population: Bonytails are the rarest of the four endangered fish in the Colorado River basin. There are no known reproducing populations in the wild.

Razorback suckers

Razorback suckers are brownish-green, white and yellow with a sharp edged hump on their backs. They have fleshy lips that they use to suck up their food. Their hump gives them stability when swimming in strong currents.

Length: Usually 16-18 inches long, though some have been known to grow up to 3 feet.

Diet: Insects, plankton, and plant matter.

Lifespan: Razorback suckers have have been known to live to 40 years or more.

Reproduction: Spawn in the spring at as early as 3 to 4 years old.

Population: The existing population is mainly adult fish, due to high death rates of young fish.

Threats

While western settlers valued the Colorado pikeminnow as food, calling them “white salmon” or “Colorado salmon,” they considered bonytails to be undesirable and began poisoning them in order to introduce other, nonnative species into the Colorado River. Since then the two main threats to the four species of endangered fish have been:

Introduction of Invasives: More than 40 non-native fish species have been introduced to the upper Colorado River basin, and prey on native fish and compete with the native fish for resources.

Water Development: Before the construction of dams and reservoirs, these fish were adapted to short periods of torrential flooding or very low flows and to longer periods of variable but less extreme flow conditions. The river was made of cooler water from snowmelt in the spring and early summer and warmed over the summer months. It also carried a large sediment load throughout the year. Man-made dams and barriers have disrupted river flows and degraded habitats and water quality.

Other threats include habitat degradation and modification, pesticides, and climate change. The most important feature of observed and projected climate changes in the Southwest is the impact on precipitation and water availability. Much of the area is already experiencing a severe drought, and climate change projections indicate that the region will be substantially drier in the future. These changes will have obvious consequences on stream flow in the Colorado River Basin.

Climate changes will also impact the snow pack on which river flows depend. In a region that is already experiencing water conflicts between agriculture, urban water use and ecosystem health needs, climate change will likely necessitate changes in how water is allocated and substantial investments in conservation.